Sweetening hydrocarbon distillates



IJuly 2l, 1953 G. H. wElsEMANN SWEETENING HYDROCARBON DISTILLATES 3Sheets-Sheet l Filed March., 8, 1950 m S Q E EE@ G. H. WEISEMANNSWEETENING HYDROCARBON DISTILLATES July 2l, 1953 5 Sheets-Sheet 2 FiledMaron 8, 1950 1ro .-10 'oN Nvldvoasw n Y MM M T ,R

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July 21, 1953 G. H. wl-:lsEMANN I 2,646,389

3o 4o AERATloN TIME (MINUTES) O D C O O o s Ln d' m N 'HO :l0 'ONNVidVDHSW JN V EN TOR. Ger H. Weisem ann BO/MQ/wg ATTORNEY Patented.lu-ly 2l, 1.953

e SWEETENTNGl HYDROCARBON Dls'rlLLA'rEs.

Gert H. Weisemann, Hobart, Ind., assignor to UNITED STATES. PATENTOFFICE Standard Oil Company, Chicago, Ill., a corporation of IndianaApplicati'n March s, 1950, serial No. 148,303

9 claims. (ci. 1%;29) l l This invention relates'to the rening ofhydrocarbon distillates, such as h eavy naphtha, kerosene, heater oiland furnace oil, which areV derived from the distillation of crude oilvor from cracking processes, either thermal or catalytic. Moreparticularly the invention relates to a method of treating such stockswith concentrated y potassium hydroxide solutions in the presence of acopper catalyst to remove mercaptans there'- from.

'It has heretofore been the practice to treat sour mercaptan-containinghydrocarbon distillates with alkaline solutions of various sorts toremove the mercaptans. Where low molecular weight mercaptans areinvolved as in the case of low-boiling distillates such as lightnaphthas, removal of mercaptans can be effected by simply washing withcaustic alkali, e. g., caustic soda or caustic potash. For this purposeit is usually rthe practice to employ a caustic soda 'solution of about10 to 20 percent concentration. lThe caustic solution can be regeneratedby steaming or air blowing to distil off the mercaptans or convert themto insoluble disulfides which can be separated from the causticsolution.

In the case of higher boilingA stocks, particularly kerosene and heateroils, thev removal of mumV of vcolor degradation; Another object is vtospeed up mercaptan removal by the use of-a copper catalyst inconjunction with air and caustic. Still another object isv to removeVmercaptans from sour hydrocarbon distillates by the use of air andregenerated caustic in the presence of a copper catalyst. A particularobject is to reduce `the mercaptansin sour hydrocarbon distillatesWhichboil'above the gasoline range with a' minimum of color degradationor formation of oil-soluble color bodies. l

It has been discovered that mercaptans can be removed from sourhydrocarbon distillates, even of the heater oil distillate boilingrange, i. e. 35o-650 F., without serious color formation by treatingwith a controlled amount of air or oxygen in the presence of an aqueouspotassium hydroxide solution having aconcentration in the range of about50 to 60,per cent by weight at a the mercaptans is'much more dicultbecause' f of their increased oil solubility or'higherv oilwaterpartition coeflicient due to their higher molecular Weight.' Numerousmethods have been proposed and-practiced for' removing heavy mercaptansof the type found in these higher 4boiling distillates. Alkalinesolutions containing organic solvents or so-called solutizers have beenemployed. Caustic-methanol solutions' have a similar action. Chemicalreagents which oxidize Y the mercaptansv to disulfldes in the presenceof Vthe oil have also been extensively. employed. v'Among these are thefamiliar alkaline sodium plumbite or doctor solution, alkalinehypochlorite l solutions, etc. Some attempts have been made to removemercaptans vfrom petroleum distillates by treating with anhydrouscaustic in the form of a dry powder or in solution or suspension in anorganic solvent such as methanol. When operating yin this way, however,serious color formation has resulted especially Where the treatment wasconducted at elevated temperatures', for example 150 F. and upwards. Ithas been found that to prevent color formation under these conditions ithas been necessary to carefully exclude oxygen or air.

An object of this invention is to remove mercaptans from sourhydrocarbonoils with a minitemperature'of about 80 to 125 F. (but highenough to prevent solidiflcation of caustic), at

atmospheric or superatmospheric pressure and in the presence of aparticular type of copper catalyst. Under these conditions themercaptans are converted to disulldes without the formation ofobjectionable color bodies. The oil t rened in this manner has` alsobeen found tovbe satisfactory from the standpoint of its burningcharacteristics when employed in sleeve-type burners. I The amount ofoxygen employed either as air Or'commercial oxygen is preferably aboutbe used, e. g. up to 0.5 per cent by weight basedl on-KOH, but usuallyit is not necessary to exceed 0.1 per cent. It is preferred to add thecopper in the formV of an aqueous solution ofy a copper salt such ascopper chloride, sulfate, nitrate or acetate. The copper salt solutionmay be added directlyv to the potassium hydroxideV solution if thelatter is hot enough to avoid formation of a black precipitate. Whenadded in this way, for example to boiling potassium hydroxide solution,a blue complex forms which appears to be a colloidal copper compound; in

this form and concentration the copper remains in active condition anddoes not precipitate from the potassium hydroxide treating reagent.

The copper catalyst can also be added to an intimate reaction mixture ofKOH solution and oil, the oil in this case forming the continuous phaseof an emulsion so that when the copper salt is introduced it is alsodispersed and results in the formation of active catalyst instead ofinactive black precipitate. When operating in this way the solution ofKOH is mixed with the oil, for example in a continuous mixer, during orafter which a solution of a water-soluble copper salt is introduced. Theoil and treating agent is then passed to another mixer into which air oroxygen is introduced. If desired, however, air may be introduced intoth'eoil and KOH before adding the copper catalyst, the air, oil,.KOI-land catalyst being all maintained in intimate contact until mercaptansare substantially eliminated.

, While the above methods of adding the copper catalyst work very wellwhen fresh caustic solution is used, the use of regenerated causticsolutions which contain material dissolved out of the sour hydrocarbonresults in a very large increase in the amount of copper catalystneeded. The addition of the copper catalyst to the'hot regeneratedcaustic results in the formation of a heavy precipitate and the bluecolor of the catalytically active caustic solution does not appear untilall the poison has been reacted. These reactive materials are believedto be oxygenated hydrocarbons. The heavy precipitate must be removed orit clogs the lines and the meters used in the process. I have discoveredthat the addition of the copper catalyst, as a concentrated watersolution, directly to the oil, so as to form a very fine dispersion,probably a WatVer-in-oil emulsion, before the caustic solution is addedeliminates this problem and also results in better finishedY oil colorwith less catalyst consumption than is obtainable with freshcaustic-catalyst solution addition.

` The invention is illustrated by the drawings which form a part of thisspecification and in which:

Figure 1 is a schematic diagram of an apparatus suitable for carryingout the process, and

Figures 2 and 3 are graphs of data illustrating the results obtained inthe process. Y

It has been found that the use of a copper catalyst results in aphenomenal increase in the mercaptan oxidation reaction rate withmarkedly 4 stood but is thought to be due in part to the oxidation ofphenolic substances contained in high sulfur oils. This effect isapparent from the data shown graphically in Figure zobtained by treating500 cc. of a sour West Texas heater' oil with 1% by volume of KOHsolution at 120o F. and air at the rate of 4.85 cubic feet per hour. Theupper curve shows rapid formation of color, i. e. decrease in SayboltUniversal color values as the mercaptan number of the oil is reducedwhen` treated with air and regenerated 55 per cent KOH. The lower curveillustrates the improved-results obtained with the same KOH solutioncontaining 0.1 per cent by weight of CuCl2.2I-l2O. n

In the operation of my process, it is important to control'thetemperature within the range of about 80 to 125 F. if a product ofsatisfactory color is to 'be obtained. Higher temperatures have beenfound to increase color formation. The following data show the effect oftemperature on the reaction, particularly with respect to mercaptannumber and color. The treats Were made by using straight-run West Texasheater oil having a -1-16 color and a mercaptan number'of 65. Thetreating reagent was a 55 per cent aqueous KOH solution containing 0.1per cent CuCl2.2H-2O, the ratio of solutionV to oil being l per cent byvolume. The oil and solution werel vigorously agitated in the presenceof air. The following results were obtained:

Color, Saybolt Time,

1 Data interpolated.

improved Saybolt coloi` as is shown by the fol- @1101221520 Mel'itfmColglay' lowing tabulated data. The aeration times to Minutes Num erUnivelrsal reach a mercaptan number of 5 and color of the nished oilwere obtained using l volume perV g +13 cent of 55% aqueous KOH, 4.85cubic feet of air 0-3 10 1910 per hour to 500 cc. ofloil and 0.1% byweight, 60 12 lgon caustic, of CuCl2.2H2O addition. 23 9'9 iz 1o 7.4 1215 4.5 9 No Catalyst Catalyst Added 5 i3. 1 12 o F Y 0 1 s 10.3 12 -7 108.3 12 Minutes Color Minutes Color l5 3.2 9 s 17.3 12 005 1o 13.5 11 NotAttamabia. 14 +10 15 10. s 9 150 -24 9 +10 s 23.7 1o 4 +10 001 10 19.6 92 +4 15 13.1 7

It has been found that the use of the copper catalyst tends to preventcolor formation, apparently by directing the oxidation reaction towardthe conversion of mercaptans to disulfides. The cause of color formationis not fully under- It is to be noted that the maximum oxidation rateoccurred with Aa copper concentration of about 0.1 to 0.2 per centCuCl2.2H2O. It is also to be noted that the oi1 obtained under theseconditions showed an improved color.

l input was 51.85 cubicn feet per hour.

It is ldesirable to separate lthe oilfrom the caustic solution afterarcontact time vof about 25 to 40 minutes in order to avoid colorformation and a contact time greater than one hour has beenfound todecrease the Saybolt color value from 16 to 5 or lower. Usually aContact time of to 30 minutes is sufficient, depending largely on thetemperature. 1

The ratio of caustic solution to oil may be varied over' a range from0.5 per cent by volume to or 15 per cent by volume, although about 5per` cent by volume has been found to give best results in the case ofheater oil from West Texas crude. When employing only 1 per cent KOHsolution, the problem of separating the spent KOH solution from the oilis more difficult than when larger volumes of solution are used. Theveffect of coalescing the treated oil is particularly valuable in thecase of low KOH-oil ratios as will be observed from the following table:y

Heater oil treated with/55% KOH and air in presence of copper catalystColor-Saybolt YUniversal Untreated oil.` i y17 Settled to remove spentKOH solution 9 Coalesced ;1 13 Coalesced and washed withwater 16 readilywhereas the NaOl-I becomes emulsied or f dissolved in the heavy oil andis difficult to rey move, even in the subsequent water washingoperation.

Figure 3 illustrates the superior action of AKOH in comparison with NaOHsolutions. The aeration time for reduction in mercaptan numberrlsconsiderably greater for NaOH solution of the same concentration. Thusthe aeration time required to reduce the mercaptan number from 80 to.60was approximately 48 minutes with 25 per cent NaOH and only 24.- minuteswith KOH solution of the same concentration.

Figure 3 also shows the effect of concentration on rate of mercaptanoxidation and it will be noted that there is atendency-for the oxidationto cease entirely or level off at a given mercaptan number depending onthe concentration. Thus 40 per cent KOH leveled off at Ythe mercaptannumber'of yabout 22, whereas 50 per cent KOH permitted the mercaptannumber rto bev reduced to about 7. These data were obtained with 500 cc.samples of a West Texas heater oil havinga' mercaptan number of 80,contacted with -airjand 1 per centbyvolume of the caustic solutioncontaining 0.1 per cent CuCl2.2H2O. The temperature of contacting was 85F. and the rate of air The odor of the oil treated by my KOH-airoxidation process has been found to be satisfactory for marketingrequirements if the oxidation per sulfate) based on; oil treated,mercaptan numbers have been reduced to about 1 or prac` tically VZeroand treated products or .good odor have been obtained with a Sayboltcolor of 15 to 17 and with good color stability and excellent burningqualities.

While the above data were taken from bench scale work using freshcaustic with the copper catalyst added to the caustic solution, pilotplant work using regenerated caustic shows the superiority of adding thecopper catalyst directly to the sour oil before the introduction of thecaustic solution. The following data were obtained on a West Texasheater .oil of about mercaptan number and about |16 Saybolt color. Inall cases the treating reagent was a 55% aqueous KOH solution, about 5parts of this solution was used per 100 parts ofthe sour oil; and allruns were made at about F.

C ase 011 aus 10 f Product Product Coppidded. Mercaptan Color AS Cop,No. saybolt ousolsmo. per.

o. 5 0.13 o. 3 +4 o. 5 0.13 3. 5 +8 0- 2 0.05 2. 2 +15 0.2 o. o5 o. tv+9 0- l 0. 03 0. 5 +9 0.1 o. o3 o. 3 +8 0. 05 0. 01 0, 5v +12 These datashow that muchless copper catalyst is needed when the catalyst is addedto the oil to get a finished oil that is nearly sweet and at the sametime is of better color by 4 or 5 .points on the Best results areobtained when the catalyst I solution is injected into sour oil in sucha manner 4that the solution is dispersed throughout the oil in very nedroplets. Preferably the dispersion should be so ne that a water-in-oilemulsion is formed. `The'dispersed copper compound apparently reactswith the KOH solution to form a catalytically active copper compoundwhich is nely dispersed throughout the oil; this dispersion may be anexplanation of the fact that less catalyst is needed when the coppersolution is added to the oil than when it is added to fresh KOHsolution.

A fuller understanding of the treating process will be obtainedfrom-Figure l wherein the principal reaction vessel is indicated by Aand the used is carried to a point where the mercaptan number is belowabout 5. (The mercaptanv number is the number of milligrams Aofmercaptan sulfur per cc. of oil, usually determined by titration with astandardized copper solution.) By employing about 5 volume per cent ofcaustic solution (55%y concentration and containing about .02 weight percent of copper in the form of Iactive colloidal copper complex butintroduced as aqueous 'cop- .KOH` reconcentrator by B. Coalescers C andD are providedrfor complete removal of caustic from the oil and E is asettler for removing wash water from the treated oil. Referring toFigure 1, the sour oil, which may be given a preliminary wash with analkaline solution, such as sodium hydroxkthrough meter l the sour oilpasses through line 8 to mixer 9l which is indicated to be of theorifice type. Air is-'introduced' by line y"land `owsr through meter I lto line 8 and thence to mixer 9. The copperv catalyst, preferablyCuSO4.5H2O or CuCl2.2H2O, in an amount of about 0.1 .Weight per cent onthe caustic solution, is introduced in the form of a concentrated watersolution, such as 10%, by line I2 and pump I3 into line 8 where 'thesolution is finely dispersed throughout the sour oil. An aqueous KOHsolution of about 55 concentration is introduced by line l'into line 8and thence to mixer 9. The KOH solution, the lair and the souroil-copper catalyst emulsion are thoroughly mixed in mixer 9, a suitableresidence time being about 35 seconds.

The resulting mixture ows by line Il to reactor A Where partialseparation of KOH solution takes place. Oil and unused air pass by lineI3 to air separator I9 from which the air is discharged by line 2). Itis preferred to maintain the reactor A under pressure, for example about100 p. s. i. g., reducing the pressure by valve 2| to about p. s. i. g.to facilitate separation of air in Aseparator i9. The use of pressureWith air increases the rate of oxidation, and pressures in the range ofto 200 p. s. i. g. are satisfactory.

Where oxygen is used, vsuperatmospheric pressure is not ordinarilyrequired. From separator 9 the oil flows by line 22 to coalescer C whichis packed with a fibrous or nely granular material such as glass Wool,rock Wool, sand, etc., providing an extensive surface for the removal ofcolloidally suspended KOH solution from the oil. The coalescer may be ahorizontal drum packed with glas-s Wool, as indicated, connected withsettling chamber 23, or it may be a packed-vertical drum, preferablyarranged for downflow of oil through the packing With a separatingchamber at the bottom. By eiecting a more rapid and complete removalofKOH, the coalescer serves to arrest the development of color in thepresence of the KOH solution.

From coalescer C the oil flows by line 24 to a second'stage coalescer D.The residence time of the oil in the coalescers is suitably about 5 tol0 minutes. From coalescer D the oil iiows by line 25 to Water mixer 26,Water being introduced into the oil stream by line 2l. Mixer 25 of theorifice type is shown, although any suitable eicient mechanical mixermay be substituted therefor. The amount of Water introduced may suitablybe 'about 5 to l0 per cent of the volume of the oil.

The water-oil mixture is conducted by line 20 to Water settler E fromwhich waste Water is withdrawn by lineY 29. Washed oil ioWs by line towater coalescer 3l, the nished oil being discharged from the system byline 32. Waste Waiter from the coalescer is discharged by line 33.

From reactor A, spent KOH is withdrawn by line 34 to settler 35 Wherepotassium cresylates are allowed to collect as an upper layer. Theseparated KOH is withdrawn by line 36 and pump 31 and thence flows byline 38 to reconcentrator B Where it is heated by submerged steam coil3Q to drive off Water which tends to accumulate in the system,particularly as a by-product of the sweetening reaction. Watereliminated as vapor is passed by line Il!) to condenser 4! and isdischarged from the system by line 6.2. The reconcentrated KOH -ows byline 43 to cooler 44 and thence by line d5 to KOH solution nlters 46which remove potassium carbonate and any other insoluble products whichmay collect in the reagent.

. The KOH solution then flows by line 41 and pump d8 back to mixer S byline i6. Makeup KOH is `supplied tothe .system from time to time by line49 as needed. If desired, concentrator B may be 8. operated underreduced pressure, e. g. 5 p. s. i. a. and consequently the temperaturecan be held below about 280 F. thereby largely avoiding decomposition ofmercaptides to KzS which is undesirable because Yit separates and clogsthe system. Such decomposition also represents a loss of KOH.

From the coalescers C and D, separated KOH solution is conducted by line50 to separator 35. The cresylate layer from separator 35 is conductedby line 5l to lseparator 52 which may be a storage tank providing anextended time for settling out aqueous caustic. It has been found thatthe small amount of caustic insoluble copper compounds formed byreaction between the copper catalyst and reactive hydrocarbons ispreferentially soluble in the cresylates and passes out of the systemwith the cresylate layer from separator 35; this fact eliminates theneed for special measures to prevent clogging of lines and meters. Therecovered KOH is conducted periodically by line 53 to the KOH line 36.If desired separator 52 can be provided with suitable means for heatingthe cresylates and thereby facilitating the separationof the KOH. Thesettled potassium cresylates are discharged from the system by line 54.

The finished oil contains a trace of copper .but not more thanY about Vlpart per million. The effect of this minute amount of copper on thecolor stability of the oil can be readily offset by the addition of asmall amount of metal deactivator, e. g. 0.001 to `0.01% ofN,N-disalicylidine-1,2-diaminopropane.

While a particular system for using the invention has been described inconsiderable detail, many modications and alternative procedures andconditions will be apparent from the above description to those skilledin the art. The

' amounts of catalyst specified in the accompanying claims refer tocopper in the form of an active compound or complex believed to becolloidal 0X- ide; such catalyst is preferably prepared as herein`described using, for example, copper sulfate which has been found toVgive outstandingly good results.

l claim:

l. The process of removing mercaptans from sour hydrocarbon distillatewhich is higher boiling than gasoline Without formation of excessivecolor therein, which comprises dispersing a copper catalyst in thedistillate, intimately contacting said catalyst-containing distillatewith about l to 15 per cent by volume of an aqueous solution of KOHhaving a concentration of about 50 to S0 per cent, said copper catalyst,which ranges from about 0.004 to 0.1 per cent by Weight of copper basedon the caustic solution, forming a catalytically active copper compoundwhen contacted With the caustic solution, introducing a gas containingan amount of free oxygen about stoichiometrically equivalent to theamount of mercaptans present in said distillate into the mixture ofcatalyst-containing distillate and KOH, `maintaining the temperature ofcontacting at about to 125 F. until a substantial reduction in mercaptancontent has been obtained and separating spent KOH solution andassociated reaction products from the treated oil.

2. The process of sweetening a sour hydrocarbon distillate which isAhigher boiling than gasoline Without formation of excessive colortherein which comprises dispersing a copper compound in the distillatewhich Will range from about 0.004 to 0.1 per cent by Weight of copper onthe caustic solution hereinafter described in the form of acatalytically active copper compound, intimately contacting saidcatalyst-containing distillate with about 5 to 10 per cent-by volume ofan aqueous solution of KOH having a concentration of about 50 to 60 percent, introducing into the reaction mixture air containing an amount ofoxygen stoichiometrically equivalent to about one and one-half to twoand one-half times the amc-unt of mercaptans present in saiddistillate,l

comprises dispersing a concentrated aqueous solui tion of coppersulfate, which solution contains between about 0.01 and 0.05 weightpercent of copper based on aqueous KOH solution used in the process'inthe distillate, intimately contacting said copper sulfate-containingdistillate with about per cent by volume of a concentrated potassiumhydroxide solution of about 50 to 60 perV cent concentration, saidcopper compound forming with the potassium hydroxide solution a coppercatalyst which is active as an oxidation catalyst, and with added freeoxygen in an amount stoichiometrically equivalent to about one andone-half to two and one-half times the amount of mercaptans present insaid distillate, continuing said contacting at a temperature in therange of about 80 to 125 F. under a pressure in the range of atmosphericto 200 pounds per square inch for between about 5 and 30 minutes, thenAseparating spent potassium hydroxide solution with reaction productscontained therein from the treated oil, separating potassium cresylatesfrom the withdrawn solution, then subjecting the solution todistillationat low pressure and at a temperature not exceeding about 300 F. for re-`moving water therefrom, and returning the concentrated caustic solutionfor contacting withV additional amounts of said distillate.

5. The process of claim 1 wherein said distillate is a sour virginheater oil distillate.

6. The process of claim 1 wherein said copper catalyst is selected fromthe group consisting of copper chloride, copper sulfate, copper nitrateand copper acetate.

7. The process of claim 2 wherein said` copper compound isselected fromthe group consisting of copper chloride, copper sulfate, copper nitratey and copper acetate.

8. The process of claim 4 wherein said copper compound is selected fromthe group consisting of copper chloride, coppersulfate, copper nitrateand copper acetate.

9. The process of claim 4 wherein said potassium hydroxide solution is asubstantially saturated aqueous potassium hydroxide solution.

' GERT H. WEISEMANN.

References' Cited in the le of this patent UNITED STATES PATENTS NumberName Date 723,368 Colin Mar. 24, 1903 1,627,055 Morrell et al May 3,1927 1,749,240 Black Mar. 4, 1930 1,789,335 Fischeret al. Jan. 20, 19312,457,635 Bond Dec. 28, 1948

1. THE PROCESS OF REMOVING MERCAPTANS FROM SOUR HYDROCARBON DISTILLATEWHICH IS HIGHER BOILING THAN GASOLINE WITHOUT FORMATION OF EXCESSIVECOLOR THEREIN, WHICH COMPRISES DISPERSING A COPPER CATALYST IN THEDISTILLATE, INTIMATELY CONTACTING SAID CATALYST-CONTAINING DISTILLATEWITH ABOUT 1 TO 15 PER CENT BY VOLUME OF AN AQUEOUS SOLUTION OF KOHHAVING A CONCENTRATION OF ABOUT 50 TO 60 PER CENT, SAID COPPER CATALYST,WHICH RANGES FROM ABOUT 0.004 TO 0.1 PER CENT BY WEIGHT OF COPPER BASEDON THE CAUSTIC SOLUTION, FORMING A CATALYTICLLY ACTIVE COPPER COMPOUNDWHEN CONTACTED WITH THE CAUSTIC SOLUTION, INTRODUCING A GAS CONTAININGAN AMOUNT OF FREE OXYEN ABOUT STOICHIOMETRICALLY EQUIVALENT TO THEAMOUNT OF MERCAPTANS PRESENT IN SAID DISTILLATE INTO THE MIXTURE OFCATALYST-CONTAINING DISTILLATE AND KOH, MAINTAINING THE TEMPERATURE OFCONTACTING AT ABOUT 80 TO 125* F. UNTIL A SUBSTANTIAL REDUCTION INMERCAPTAN CONTENT HAS BEEN OBTAINED AND SEPARATING SPENT KOH SOLUTIONAND ASSOCIATED REACTION PRODUCTS FROM THE TREATED OIL.